Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c - bisected

[Alan D. Brunelle]

Linus Torvalds wrote:
> 
> On Mon, 25 Aug 2008, Linus Torvalds wrote:
>> But I'll look at your vmlinux, see what stands out.
> 
> Oops. I already see the problem.
> 
> Your .config has soem _huge_ CPU count, doesn't it?
> 
> checkstack.pl shows these things as the top problems:
> 
> 	0xffffffff80266234 smp_call_function_mask [vmlinux]:    2736
> 	0xffffffff80234747 __build_sched_domains [vmlinux]:     2232
> 	0xffffffff8023523f __build_sched_domains [vmlinux]:     2232
> 	0xffffffff8021e884 setup_IO_APIC_irq [vmlinux]:         1616
> 	0xffffffff8021ee24 arch_setup_ht_irq [vmlinux]:         1600
> 	0xffffffff8021f144 arch_setup_msi_irq [vmlinux]:        1600
> 	0xffffffff8021e3b0 __assign_irq_vector [vmlinux]:       1592
> 	0xffffffff8021e626 __assign_irq_vector [vmlinux]:       1592
> 	0xffffffff8023257e move_task_off_dead_cpu [vmlinux]:    1592
> 	0xffffffff802326e8 move_task_off_dead_cpu [vmlinux]:    1592
> 	0xffffffff8025dbc5 tick_handle_oneshot_broadcast [vmlinux]:1544
> 	0xffffffff8025dcb4 tick_handle_oneshot_broadcast [vmlinux]:1544
> 	0xffffffff803f3dc4 store_scaling_governor [vmlinux]:    1376
> 	0xffffffff80279ef4 cpuset_write_resmask [vmlinux]:      1360
> 	0xffffffff803f465d cpufreq_add_dev [vmlinux]:           1352
> 	0xffffffff803f495b cpufreq_add_dev [vmlinux]:           1352
> 	0xffffffff803f3fc4 store_scaling_max_freq [vmlinux]:    1328
> 	0xffffffff803f4064 store_scaling_min_freq [vmlinux]:    1328
> 	0xffffffff803f44c4 cpufreq_update_policy [vmlinux]:     1328
> 	..
> 
> and sys_init_module is actually way way down the list. I bet the only 
> reason it showed up at all was because dynamically it was such a deep 
> callchain, and part of that callchain probably called some of those really 
> nasty things.
> 
> Anyway, the reason smp_call_function_mask and friends have such _huge_ 
> stack usages for you is that they contain a 'cpumask_t' on the stack.
> 
> For example, for me, usign a sane NR_CPU, the size of the stack frame for 
> smp_call_function_mask is under 200 bytes.  For you, it's 2736 bytes.
> 
> How about you make CONFIG_NR_CPU's something _sane_? Like 16? Or do you 
> really have four thousand CPU's in that system?
> 
> Oh, I guess you have the MAXSMP config enabled? I really think that was a 
> bit too aggressive.
> 
> 		Linus

This probably all started when I was working on a software tool (aiod)
that was failing because somebody ELSE had 4,096 CPUs configured.
[[Seems that gcc had/has? it's MAX CPU value set to 1,024 (bits/sched.h
__CPU_SETSIZE), so when you issue system calls like sched_getaffinity,
it will "fail" for systems configured w/ 4,096 CPUs. I worked around it
by simply forgetting about the gcc values, and kept allocating larger
CPU masks until it worked.]]

I think you're right: the kernel as a whole may not be ready for 4,096
CPUs apparently...

Thanks for taking the time to look into this...

Alan
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